Leeks with a solid core
I’m thinking you may have an early maturing variety of leek as towards the end of the season leeks start to develop a hard core in the middle which is the stem of their flower; if they are bolting you can find this solid core even in the autumn. Early on it can be soft enough to use, especially in soups, but after the New Year it is likely to be tough and will have to be discarded. Once your leeks have reached the stage of being mostly hard core and tough outer leaves it is time to relegate them to the compost.
Leeks are available to buy from late summer through to early spring and, by choosing varieties that mature in succession, you can dig them from the garden for at least six months of the year.
Examples of varieties available for succession growing:-
Swiss Giant Zermatt – Early variety, harvest late summer/autumn
Hannibal – Early autumn harvest
De Carentan – Harvest October to January
Kenton F1 - Harvest November to March
Bandit – Late variety, harvest December to April
Hope you have better luck next time.